1. Field of the Invention
This invention relates to a blood vessel imaging system for imaging blood vessels, and more particularly to a blood vessel imaging system which can image blood vessels with arteries and veins distinguished from each other. This invention also relates to a system for distinguishing arteries and veins from each other. This invention further relates to a system for measuring a frequency deviation of a measuring light beam, which has been irradiated to a scattering fluid for blood vessel imaging, or the like, due to a Doppler effect.
2. Description of the Related Art
In the clinical field, there has been a wide demand for imaging arteries and veins clearly distinguished from each other. For example, since arteriosclerosis generally starts at the periphery of the arteries, it will be useful in diagnosing arteriosclerosis if the inner walls of the peripheral arteries can be imaged distinguished from those of the veins.
There has been wide known angiography as a system for imaging blood vessels. However angiography is invasive, e.g., it involves administration of a contrast medium to the testee, which gives the testee causalgia and involves insertion of a catheter into an artery, and accordingly, it is difficult to perform angiography without staying the testee in the hospital.
Further there has been proposed technique for imaging a part of an organism on the basis of penetration of light through the part as disclosed in xe2x80x9cIEEE Journal of Selected Topics in Quantum Electronicsxe2x80x9d, Vol. 2, p1008, 1996. In this imaging method, a light beam is projected onto a finger and light which travels straight through the finger while scattered in multiple scattering in the finger is detected by optical heterodyne detection. Then a cross-sectional image of the finger is obtained by use of a method of image reconstitution which has been employed in computed tomography. However, it has been impossible to recognize existence of a blood vessel by this method.
Further, there has been proposed technique in which the hollow of a hand is illuminated by light emitted from a plurality of LEDs and an image of blood vessels on the back side of the hand formed by light scattered inside the hand is taken as animation by a sensitive TV camera as disclosed in xe2x80x9cJapanese ME Academy Magazine BMExe2x80x9d, vol.8, No.5, pp.41, 1994. However, only subcutaneous veins or blood vessels in a relatively shallow part of the hand can be imaged by the technique and it is impossible to image arteries and veins clearly distinguished from each other by the technique.
In view of the foregoing observations and description, the primary object of the present invention is to provide a blood vessel imaging system which can image peripheral blood vessels such as peripheral arteries and the like in a relatively deep part of the hand or foot with the blood vessels clearly distinguished from other soft tissues and can image blood vessels with arteries and veins clearly distinguished from each other without exposing the testee to heavy load.
Another object of the present invention is to provide a system which can clearly distinguish arteries and veins from each other without exposing a testee to heavy load.
The specific object of the present invention is to provide a system which can measure a frequency deviation of a measuring light beam, which has been irradiated to a scattering fluid, due to a Doppler effect.
In blood vessel imaging systems in accordance with one aspect of the present invention, a blood vessel is basically imaged by projecting a measuring light beam onto an organism and detecting light scattered by the organism. A light homodyne detection system is applied in detecting the scattered light, thereby distinguishing an artery and a vein from each other on the basis of difference in flow rate of the blood between the artery and the vein. Further by combining the light homodyne detection system with an optical heterodyne detection system, the beat components of light detected by the light homodyne detection system are amplified.
That is, in accordance with a first aspect of the present invention, there is provided a blood vessel imaging system comprising
a measuring light source which emits a measuring light beam,
an optical homodyne interference system which splits first and second light beams from the measuring light beam, causes the first and second light beams to impinge upon the same irradiating point on an organism in different directions, and combines together the first and second light beams scattered at the irradiating point into a combined scattered light beam,
a scanning means which causes the first and second light beams to scan the organism,
an optical heterodyne detection system consisting of an optical heterodyne interference system which splits a third light beam from the measuring light beam and combines the third light beam with the combined scattered light beam emanating from the optical homodyne interference system into a combined output light beam, a frequency shifter which causes a frequency difference between the third light beam and the first and second light beams, and a beat component detecting means which detects beat components of the combined output light beam and outputs a beat component detection signal, and
an image signal generating means which generates an image signal on the basis of the frequency of the beat components, generated by the optical homodyne interference system, included in the beat component detection signal output from the optical heterodyne detection system.
For example, the image signal generating means generates an image signal representing artery parts of the organism when the frequency of the beat components generated by the optical homodyne interference system is higher than a predetermined threshold value, and generates an image signal representing vein parts of the organism when the frequency of the beat components generated by the optical homodyne interference system is not higher than the predetermined threshold value.
It is preferred that the blood vessel imaging system be provided with a position adjustment means which adjusts the positions of the organism and the optical homodyne interference system relative to each other to change the directions of incidence to the irradiating point of the first and second light beams.
It is preferred that the blood vessel imaging system be provided with an in-phase time detecting means for detecting in-phase times, at which the flow rate of blood in the blood vessel to be imaged becomes a predetermined value, and outputting a timing signal, and the image signal generating means samples the beat component detection signal at times, at which the flow rate of the blood is substantially maximized, on the basis of the timing signal and generates the image signal on the basis of the sampled beat component detection signal.
The in-phase time detecting means may be, for instance, a means for detecting the pulse wave of the organism, or a means for detecting the times at which the frequency of the beat components generated by the optical homodyne interference system takes a peak value.
When fluid is flowing in the irradiating point upon which the first and second light beams impinge in different directions, the frequencies of the first and second light beams scattered at the irradiating point are deviated by a Doppler effect.
Assuming, for the purpose of simplicity, that one of the first and second light beams passes through one of two points on a plane facing the organism and travels along an optical path passing through the optical axis after scattered and reflected by the organism and the other of the first and second light beams passes through the other of two points and travels along an optical path passing through the optical axis after scattered and reflected by the organism, frequency deviation of said one of the first and second light beams is xcex94f and that of the other is xe2x88x92xcex94f when the reflecting point has a velocity component. When the scattered first and second light beams are combined, a beat component at a frequency of 2xcex94f is generated by interference in the combined scattered light beam.
Accordingly, when existence of a beat component at a frequency of 2xcex94f is detected for each scanning point of the measuring light beam (the first and second light beams) and the image signal generating means is arranged to generate, an image signal component bearing thereon a relatively high density when the beat component is detected and an image signal component bearing thereon a relatively low density when the beat component is not detected, the part through which fluid is flowing, that is, the blood vessel part, can be imaged at a high density whereas other soft tissues are imaged at a low density.
The artery part and the vein part can be distinguished from each other in the following manner. That is, the frequency deviation xcex94f is in proportion to the flow rate of the fluid and the flow rate of blood is higher in arteries than in veins. Accordingly, the frequency deviation xcex94fa when the measuring light beam is projected onto an artery is larger than the frequency deviation xcex94fv when the measuring light beam is projected onto a vein. Accordingly, when a suitable threshold value is set with respect to the frequency 2xcex94f of the beat component detection signal (beat signal), and the image signal generating means is arranged so that it generates an image signal representing an artery part when the beat signal frequency 2xcex94f is higher than the threshold value and generates an image signal representing a vein part when the beat signal frequency 2xcex94f is not higher than the threshold value, the artery part and the vein part can be imaged distinguished from each other.
When the image signal generating means is arranged to generate an image signal bearing thereon a density which is higher as the value of the beat signal frequency 2xcex94f becomes higher without use of a threshold value, the artery part and the vein part can be imaged so that they can be distinguished from each other by density (brightness).
Since the measuring light beam scattered by a blood vessel is inherently very weak, the beat signal is also very weak. However, in the blood vessel imaging system of the present invention, since the beat signal output from the optical heterodyne detecting system is detected, the amplitude of the signal representing the beat components generated by the optical homodyne interference system is superimposed with the beat components generated by the optical heterodyne detection system and is theoretically amplified to (A2/A1)xc2xd times wherein A1 represents the amplitude of the beat signal by the homodyne detection system and A2 represents the amplitude of the beat signal by the heterodyne detection system. Since the amount of light in the heterodyne detecting system can be freely set, the beat signal can be detected at a high S/N ratio by properly setting the amount of light, whereby even a peripheral artery or the like deep in the hand or foot can be clearly imaged.
Further, when a position adjustment means which adjusts the positions of the organism and the optical homodyne interference system relative to each other to change the directions of incidence to the irradiating point of the first and second light beams is provided, the beat signal can be detected at a higher S/N ratio.
That is, assuming that the first and second light beams impinge upon the organism passing through two points on a plane opposed to the organism, the amplitude of the beat signal generated by the optical homodyne interference system is maximized when the flow of blood is in a direction parallel to the straight line joining the two points. By setting the directions of incidence of the first and second light beams to be parallel to the flow of blood by operating the position adjustment means, a high level beat signal can be obtained.
When so setting the directions of incidence of the first and second light beams, it is not necessary to watch the directions of incidence and the direction of the flow of blood but the position adjustment means has only to be operated so that the intensity of the beat signal is maximized.
The flow rate of arterial blood varies with pulsation and sometimes becomes very close to that of the venous blood. Accordingly, when the beat components are detected at the minimum flow rate of arterial blood, an artery and a vein sometimes cannot be clearly distinguished from each other.
When the blood vessel imaging system is provided with an in-phase time detecting means for detecting in-phase times, at which the flow rate of blood in the blood vessel to be imaged becomes a predetermined value, and outputting a timing signal, and the image signal generating means samples the beat component detection signal at times, at which the flow rate of the blood is substantially maximized, on the basis of the timing signal and generates the image signal on the basis of the sampled beat component detection signal, the image signal can be constantly generated on the basis of a beat signal at a time at which the flow rate of the arterial blood is maximized, whereby the aforesaid problem can be avoided.
In blood vessel imaging systems in accordance with another aspect of the present invention, a blood vessel is basically imaged by projecting a measuring light beam onto an organism and detecting light scattered by the organism. An artery and a vein are distinguished from each other on the basis of difference in direction of flow of blood between the artery and the vein by use of an optical interference system. Further by combining the light homodyne detection system with the optical interference system, the beat components of light detected by the optical interference system are amplified.
That is, in accordance with a second aspect of the present invention, there is provided a blood vessel imaging system comprising
a measuring light source which emits a measuring light beam,
an optical interference system consisting of a first optical system which splits first and second light beams from the measuring light beam, causes the first and second light beams to impinge upon the same irradiating point on an organism in different directions, and combines together the first and second light beams scattered at the irradiating point into a combined scattered light beam, and a first frequency shifter which causes a frequency difference between the first and second light beams,
a scanning means which causes the first and second light beams to scan the organism,
an optical heterodyne detection system consisting of a second optical system which splits a third light beam from the measuring light beam upstream of the first optical system and combines the third light beam with the combined scattered light beam emanating from the first optical system into a combined output light beam, a second frequency shifter which causes a frequency difference between the third light beam and the measuring light beam from which the third light beam is split, and a beat component detecting means which detects beat components of the combined output light beam and outputs a beat component detection signal, and
an image signal generating means which generates an image signal on the basis of the frequency of the beat components, generated by the optical interference system, included in the beat component detection signal output from the optical heterodyne detection system.
For example, the image signal generating means generates an image signal representing artery parts of the organism when the frequency of the beat components generated by the optical interference system is higher than a predetermined threshold value, and generates an image signal representing vein parts of the organism when the frequency of the beat components generated by the optical interference system is not higher than the predetermined threshold value.
It is preferred that the blood vessel imaging system be provided with a position adjustment means which adjusts the positions of the organism and the optical interference system relative to each other to change the directions of incidence to the irradiating point of the first and second light beams.
Instead of providing such a position adjustment means, an additional optical interference system having the same arrangement as said (first) optical interference system may be provided so that the directions in which the first and second light beams of one of the optical interference systems impinge upon the irradiating point are directions which extend along an x-direction on a plane opposed to the irradiating point when projected onto the plane, and the directions in which the first and second light beams of the other of the optical interference systems impinge upon the irradiating point are directions which extend along a y-direction perpendicular to the x-direction on said plane when projected onto the plane, and in this case, the image signal generating means generates an image signal on the basis of the value of fx2+fy2 wherein fx and fy represent the frequency deviations of the beat components generated by the respective optical interference systems.
Also, instead of providing such a position adjustment means, an additional optical interference system having the same arrangement as said (first) optical interference system may be provided so that the directions in which the first and second light beams of one of the optical interference systems impinge upon the irradiating point are directions which extend along a straight line on a plane opposed to the irradiating point when projected onto the plane, and the directions in which the first and second light beams of the other of the optical interference systems impinge upon the irradiating point are directions which extend along a direction making an angle of xcex8, where 0xc2x0 less than xcex8 less than 90xc2x0, with said straight line on said plane when projected onto the plane, and in this case, the image signal generating means generates an image signal on the basis of the values of fxxe2x80x2 and fyxe2x80x2 wherein fxxe2x80x2 and fyxe2x80x2 represent the frequency deviations of the beat components generated by the respective optical interference systems. It is preferred that also the blood vessel imaging system in accordance with the second aspect of the present invention be provided with an in-phase time detecting means for detecting in-phase times, at which the flow rate of blood in the blood vessel to be imaged becomes a predetermined value, and outputting a timing signal, and the image signal generating means samples the beat component detection signal at times, at which the flow rate of the blood is substantially maximized, on the basis of the timing signal and generates the image signal on the basis of the sampled beat component detection signal.
The in-phase time detecting means may be, for instance, a means for detecting the pulse wave of the organism, or a means for detecting the times at which the frequency of the beat components generated by the optical homodyne interference system takes a peak value. As described above, when fluid is flowing in the irradiating point upon which the first and second light beams impinge in different directions, the frequencies of the first and second light beams scattered at the irradiating point are deviated by a Doppler effect.
Assuming, for the purpose of simplicity, that one of the first and second light beams passes through one of two points on a plane facing the organism and travels along an optical path passing through the optical axis after scattered and reflected by the organism and the other of the first and second light beams passes through the other of the two points and travels along an optical path passing through the optical axis after scattered and reflected by the organism while the frequency of said one of the first and second light beams is xcfx89+xcex94xcfx89 and the frequency of said the other of the first and second light beams is xcfx89 (xcex1xcfx89 is the amount of the frequency shift by the first frequency shifter), frequency of said one of the first and second light beams is shifted to xcfx89+xcex94xcfx89+fa (fa being the amount of frequency deviation) and that of the other is shifted to xcfx89xe2x88x92fa. When the scattered first and second light beams are combined, a beat component at a frequency of {(xcfx89+xcex94xcfx89+fa)xe2x88x92(xcfx89xe2x88x92fa)}=xcex94xcfx89+2fa is generated by interference in the combined scattered light beam. When the direction of flow of the fluid is reverse and the amount of frequency deviation at that time is represented by fv, a beat component at a frequency of {(xcfx89+xcex94xcfx89xe2x88x92fv)xe2x88x92(xcfx89+fv)}=xcex94xcfx89xe2x88x922fv is generated by interference in the combined scattered light beam.
Since in the finger and the like, arterial blood and venous blood flow substantially in opposite directions, the frequency of the beat components when the measuring light beam (the first and second light beams) is being projected onto an artery part differs from that when the measuring light beam (the first and second light beams) is being projected onto a vein part in the manner described above.
Accordingly, when a suitable threshold value, e.g., equivalent to xcfx89, is set with respect to the frequency of the beat component detection signal (beat signal), and the image signal generating means is arranged so that it generates an image signal representing an artery part when the beat signal frequency is higher than the threshold value and generates an image signal representing a vein part when the beat signal frequency is not higher than the threshold value, the artery part and the vein part can be imaged distinguished from each other.
Depending on the relation of the directions of incidence of the first and second light beams and the directions of flow of arterial blood and venous blood, the frequency of the beat component detection signal is deviated to reduce the amount of frequency shift xcex94xcfx89 when the first and second light beams are projected onto an artery part and to increase the amount of frequency shift xcex94xcfx89 when the first and second light beams are projected onto a vein part conversely to the case described above.
When the image signal generating means is arranged to generate an image signal bearing thereon a density which is higher as the value of the beat signal frequency becomes higher without use of a threshold value, the artery part and the vein part can be imaged so that they can be distinguished from each other by density (brightness).
Since the measuring light beam scattered by a blood vessel is inherently very weak, the beat signal is also very weak. However, in the blood vessel imaging system of the present invention, since the beat signal output from the optical heterodyne detecting system is detected, the amplitude of the signal representing the beat components generated by the optical interference system is superimposed with the beat components generated by the optical heterodyne detection system and is theoretically amplified to (A2/A1)xc2xd times wherein A1 represents the amplitude of the beat signal by the optical interference system and A2 represents the amplitude of the beat signal by the heterodyne detection system. Accordingly, the beat signal can be detected at a high S/N ratio and even a peripheral artery or the like deep in the hand or foot can be clearly imaged.
Further, when a position adjustment means which adjusts the positions of the organism and the optical interference system relative to each other to change the directions of incidence to the irradiating point of the first and second light beams is provided, the beat signal can be detected at a higher S/N ratio.
That is, assuming that one of the first and second light beams passes through one of two points on a plane facing the organism and travels along an optical path passing through the optical axis after scattered and reflected by the organism and the other of the first and second light beams passes through the other of two points and travels along an optical path passing through the optical axis after scattered and reflected by the organism, the amplitude of the beat signal generated by the optical interference system is maximized when the flow of blood is in a direction parallel to the straight line joining the two points. By setting the directions of incidence of the first and second light beams to be parallel to the flow of blood by operating the position adjustment means, a high level beat signal can be obtained.
When so setting the directions of incidence of the first and second light beams, it is not necessary to watch the directions of incidence and the direction of the flow of blood but the position adjustment means has only to be operated so that the intensity of the beat signal is maximized.
When an additional optical interference system having the same arrangement as said (first) optical interference system is provided so that the directions in which the first and second light beams of one of the optical interference systems impinge upon the irradiating point are directions which extend along a x-direction on a plane opposed to the irradiating point when projected onto the plane, and the directions in which the first and second light beams of the other of the optical interference systems impinge upon the irradiating point are directions which extend along a y-direction perpendicular to the x-direction on said plane when projected onto the plane, and the image signal generating means generates an image signal on the basis of the value of fx2+fy2 wherein fx and fy represent the frequency deviations of the beat components generated by the respective optical interference systems, a high level beat signal can be obtained irrespective of the directions of incidence of the first and second light beams relative to the direction of flow of blood.
That is, when there is a flow of blood in an arbitrary direction with respect to the x- and y-directions and the flow rate (velocity) is v, v2=vx2+vy2, wherein and vx represents the velocity component in x-direction and vy represents the velocity component in y-direction, as shown in FIG. 16. Since the frequency deviations fx and fy are respectively proportional to vx and vy, generation of the image signal on the basis of fx2+fy2 is equivalent to generation of the image signal on the basis of v2, or v, and is after all equivalent to generation of the image signal on the basis of the beat signal frequency when Doppler effect is generated only in the direction of the flow rate v. The case where Doppler effect is generated only in the direction of the flow rate v occurs when the directions of incidence of the first and second light beams are set to be parallel to the flow of blood.
In cases where the x direction and the y direction are perpendicular to each other, the effects described above are obtained. Arteries and veins can be imaged by being distinguished from each other also with the blood vessel imaging system in accordance with the second aspect of the present invention, wherein an additional optical interference system having the same arrangement as said (first) optical interference system is provided so that the directions in which the first and second light beams of one of the optical interference systems impinge upon the irradiating point are directions which extend along a straight line (an xxe2x80x2 direction) on a plane opposed to the irradiating point when projected onto the plane, and the directions in which the first and second light beams of the other of the optical interference systems impinge upon the irradiating point are directions which extend along a direction (a yxe2x80x2 direction) making an angle of xcex8, where 0xc2x0 less than xcex8 less than 90xc2x0, with said straight line on said plane when projected onto the plane. How the effects can be obtained will be described hereinbelow.
The xxe2x80x2 direction and the yxe2x80x2 direction described above are defined as shown in FIG. 17. Also, the flow rate (velocity) component in the xxe2x80x2 direction is represented by v1, and the flow rate component in the yxe2x80x2 direction is represented by v2. The angle made between the xxe2x80x2 direction and the yxe2x80x2 direction is represented by xcex8, where 0xc2x0 less than xcex8 less than 90xc2x0, and the angle made between the xxe2x80x2 direction and the flow direction of blood is represented by xcfx86. The flow rate of blood v and the flow direction of blood xcfx86 can be calculated in the manner described below. From FIG. 17, Formulas (1) and (2) shown below obtain.                               v          1                =                              v            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            φ                    -                      v            ⁢                          xe2x80x83                        ⁢            sin            ⁢                          xe2x80x83                        ⁢            φ            xc3x97                                          cos                ⁢                                  xe2x80x83                                ⁢                θ                                            sin                ⁢                                  xe2x80x83                                ⁢                θ                                                                        (        1        )                                                                                    v                2                            =                              v                ⁢                                  xe2x80x83                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                φ                xc3x97                                                                            1                      2                                        +                                                                  tan                        2                                            ⁡                                              (                                                                              90                            ∘                                                    -                          θ                                                )                                                                                                                                                                    =                              v                ⁢                                  xe2x80x83                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                φ                xc3x97                                                      1                    +                                                                                            cos                          2                                                ⁢                                                  xe2x80x83                                                ⁢                        θ                                                                                              sin                          2                                                ⁢                                                  xe2x80x83                                                ⁢                        θ                                                                                                                                                                    =                              v                ⁢                                  xe2x80x83                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                φ                xc3x97                                  1                                      sin                    ⁢                                          xe2x80x83                                        ⁢                    θ                                                                                                          (        2        )            
From Formula (2) shown above, Formula (3) shown below obtains.
v sin xcfx86=v2 sin xcex8xe2x80x83xe2x80x83(3)
Substitution of Formula (3) into Formula (1) yields                                           v            1                    =                                    v              ⁢                              xe2x80x83                            ⁢              cos              ⁢                              xe2x80x83                            ⁢              φ                        -                                          (                                                      v                    2                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                  θ                                )                            xc3x97                                                cos                  ⁢                                      xe2x80x83                                    ⁢                  θ                                                  sin                  ⁢                                      xe2x80x83                                    ⁢                  θ                                                                    ⁢                  
                ⁢                              v            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            φ                    =                                    v              1                        +                                          v                2                            ⁢              cos              ⁢                              xe2x80x83                            ⁢              θ                                                          (        4        )            
Also, v2=(v cos xcfx86)2+(v sin xcfx86)2. Substitution of Formula (4) into this formula yields                               v          2                =                                            (                                                v                  1                                +                                                      v                    2                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  θ                                            )                        2                    +                                    (                                                v                  2                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                θ                            )                        2                                                  =                              v            1            2                    +                      2            ⁢                          v              1                        ⁢                          v              2                        ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            θ                    +                      v            2            2                              
Also, the formula shown below obtains.       tan    ⁢          xe2x80x83        ⁢    φ    =            v      ⁢              xe2x80x83            ⁢      sin      ⁢              xe2x80x83            ⁢      θ              v      ⁢              xe2x80x83            ⁢      cos      ⁢              xe2x80x83            ⁢      θ      
Substitution of Formulas (3) and (4) into this formula yields       tan    ⁢          xe2x80x83        ⁢    φ    =                    v        ⁢                  xe2x80x83                ⁢        sin        ⁢                  xe2x80x83                ⁢        θ                    v        ⁢                  xe2x80x83                ⁢        cos        ⁢                  xe2x80x83                ⁢        θ              =                            v          2                ⁢        sin        ⁢                  xe2x80x83                ⁢        θ                              v          1                +                              v            2                    ⁢          cos          ⁢                      xe2x80x83                    ⁢          θ                    
From the two formulas mentioned last, Formulas (a) and (b) shown below obtain.
v={square root over (v12+2v1v2 cos xcex8)}
+v22xe2x80x83xe2x80x83(a)
                              tan          ⁢                      xe2x80x83                    ⁢          φ                =                                            v              2                        ⁢            sin            ⁢                          xe2x80x83                        ⁢            θ                                              v              1                        +                                          v                2                            ⁢              cos              ⁢                              xe2x80x83                            ⁢              θ                                                          (        b        )            
The flow rate of blood v and the flow direction of blood xcfx86 can be calculated with Formulas (a) and (b). When the flow rate of blood v is known, as described above, the artery and the vein can be imaged by being distinguished from each other in accordance with the difference between the flow rate of blood through the artery and the flow rate of blood through the vein.
In accordance with a third aspect of the present invention, there is provided a blood vessel distinguishing system comprising
a measuring light source which emits a measuring light beam impinging upon an organism,
a first optical interference system constituted such that a frequency of first beat components, which are generated by the measuring light beam and which are detected, changes in accordance with a flow rate of blood due to a Doppler effect with the blood flow,
a second optical interference system for causing signal light and a local oscillator beam, which has been modulated with a frequency different from the frequency of the first beat components detected by the first optical interference system, to interfere with each other, and thereby generating second beat components having a frequency different from the frequency of the first beat components,
a deviation measuring means for measuring a frequency deviation of a beat signal, which is formed by the second beat components, from the modulation frequency of the local oscillator beam, and
a distinguishing means for distinguishing whether a blood vessel containing the blood flow is an artery or a vein, the distinguishing being made in accordance with relationship between a magnitude of the frequency deviation, which has been measured by the deviation measuring means, and a predetermined threshold value.
It is preferred that the blood vessel distinguishing system be provided with a position adjustment means which adjusts the positions of the organism and the first optical interference system relative to each other to change the directions of incidence to the same irradiating point of first and second light beams, into which the measuring light beam is split.
Also, the blood vessel distinguishing system should preferably be modified such that an additional first optical interference system having the same arrangement as said first optical interference system may be provided so that the directions in which first and second light beams split from the measuring light beam in one of the first optical interference systems impinge upon the irradiating point are directions which extend along a straight line on a plane opposed to the irradiating point when projected onto the plane, and the directions in which first and second light beams split from the measuring light beam in the other of the first optical interference systems impinge upon the irradiating point are directions which extend along a direction perpendicular to the straight line on said plane when projected onto the plane, and in this case, the distinguishing means determines the flow rate of blood and the flow direction of blood on the basis of the value of fx2+fy2 wherein fx and fy represent the frequency deviations of the beat components generated by the respective first optical interference systems.
Also, the blood vessel distinguishing system should preferably be modified such that an additional first optical interference system having the same arrangement as said first optical interference system may be provided so that the directions in which first and second light beams split from the measuring light beam in one of the first optical interference systems impinge upon the irradiating point are directions which extend along a straight line on a plane opposed to the irradiating point when projected onto the plane, and the directions in which first and second light beams split from the measuring light beam in the other of the first optical interference systems impinge upon the irradiating point are directions which extend along a direction making an angle of xcex8, where 0xc2x0 less than xcex8 less than 90xc2x0, with said straight line on said plane when projected onto the plane, and in this case, the distinguishing means determines the flow rate of blood and the flow direction of blood on the basis of the values of fxxe2x80x2 and fyxe2x80x2 wherein fxxe2x80x2 and fyxe2x80x2 represent the frequency deviations of the beat components generated by the respective first optical interference systems.
It is preferred that also the blood vessel distinguishing system in accordance with the third aspect of the present invention be provided with an in-phase time detecting means for detecting in-phase times, at which the flow rate of blood in the blood vessel to be distinguished becomes a predetermined value, and outputting a timing signal, and the distinguishing means samples a beat component detection signal at times, at which the flow rate of the blood is substantially maximized, and utilizes the sampled beat component detection signal for the blood vessel distinguishing.
The in-phase time detecting means may be, for instance, a means for detecting the pulse wave of the organism, or a means for detecting the times at which the frequency of the beat components generated by the first optical interference system takes a peak value.
In the aforesaid blood vessel imaging systems in accordance with the present invention, the characteristics are utilized in that the frequency deviation, which occurs when the measuring light beam impinges upon the blood vessel part, varies for the artery and the vein. In this manner, the artery is imaged by being distinguished from the vein. In the course of the imaging, the frequency deviation of the beat component detection signal (the beat signal) is calculated. Therefore, the artery and the vein can be distinguished from each other on the basis of the frequency deviation of the beat signal. With the technique described above, the blood vessel distinguishing system in accordance with the third aspect of the present invention distinguishes the blood vessels.
In accordance with a fourth aspect of the present invention, there is provided a frequency deviation measuring system comprising
a measuring light source which emits a measuring light beam impinging upon a scattering fluid,
a first optical interference system constituted such that a frequency of first beat components, which are generated by the measuring light beam and which are detected, changes in accordance with a flow rate of the scattering fluid due to a Doppler effect with the scattering fluid,
a second optical interference system for causing signal light and a local oscillator beam, which has been modulated with a frequency different from the frequency of the first beat components detected by the first optical interference system, to interfere with each other, and thereby generating second beat components having a frequency different from the frequency of the first beat components, and
a deviation measuring means for measuring a frequency deviation of a beat signal, which is formed by the second beat components, from the modulation frequency of the local oscillator beam.
As the first optical interference system described above, a system constituted of an optical homodyne interference system, a system constituted of an optical heterodyne interference system, or the like, is appropriate.
Also, the deviation measuring means should preferably be constituted so as to calculate the absolute value of the flow rate of the scattering fluid from the magnitude of the measured frequency deviation.
With the frequency deviation measuring system in accordance with the fourth aspect of the present invention, the aforesaid technique for calculating the frequency deviation is applied to the measurement of the frequency deviation with respect to scattering fluids, and the frequency deviation can be measured accurately